User talk:Gillian Setiawan/Bluntnose sixgill shark/Bibliography

Bibliography Andrews, K.S., Bargmann, G., Farrer, D., Harvey, C.J., Levin, P.S., Tolimieri, N., & Williams G.D., (2009). Diel activity patterns of sixgill sharks, Hexanchus griseus: the ups and downs of an apex predator. Animal Behaviour, 78(2) 525-536. https://doi.org/10.1016/j.anbehav.2009.05.027 This research followed the diel and seasonal patterns of vertical movement of sixgill sharks using active and passive acoustic telemetry. The researchers focused on three potential factors for causing these patterns– foraging, predator or competitor avoidance, and maintaining bioenergetic efficiency. They found that the sharks were more active in the evening and occupied shallower waters at night. These sixgill sharks were also most active in the autumn and found in deeper depths during the autumn and winter months. Researchers ruled out predator or competitor avoidance as the potential reasons for the vertical movement patterns because they found pairs of sharks with synchronized movements, indicating that the sharks were responding to the same stimuli. They also did not find any evidence of temperature usage for thermoregulation on a daily basis. In addition to these reasons, the distinct and consistent patterns of vertical migration and activities despite size, sex, and spatial scales showed that foraging behavior can most likely be seen as the reason for the diel vertical pattern of sixgill sharks.

Andrews, K.S., Levin, P.S., & William, G.D., (2010). Seasonal and ontogenetic changes in movement patterns of sixgill sharks. PLoS ONE, 5(9). doi: doi:10.1371/journal.pone.0012549 The study involved using large-scale acoustic arrays to observe the movement patterns of 34 sixgill sharks in and around Puget Sound, Washington, USA. Using the data collection that was accumulated for over four years, the researchers tried to understand the sedentary levels of sixgill sharks, seasonal patterns of sixgill sharks, and their emigration out of Puget Sound. The data analysis revealed that sixgill sharks had consistent seasonal movements by moving north during the winter and spring and south during the summer and fall. The sixgill sharks inhabit the same region for about a month before their sedentariness drops to less than 50 percent. The sedentariness continues to drop until 180 days are reached, at which point the sedentariness rises to 43 percent by 365 days. Out of the 34 sharks, 19 left Puget Sound. The researchers were also able to calculate that for every one centimeter increase in total length of a female sixgill shark, the probability of it leaving Puget Sound increased by 4.5 percent. This calculation is not applicable to male sixgill sharks. The researchers determined that these movement patterns can be attributed to the seasonal movements of prey over other reasons since there was no correlation between gender and month of movement, as well as the sixgill sharks’ status of being the largest predator of Puget Sound, making it unlikely that they are trying to escape predation.

Gonzalez-Pola, C., Rodriguez-Cabello, C., Rodriguez, A., & Sanchez, F. (2018). Insights about depth distribution, occurrence and swimming behavior of Hexanchus griseus in the Cantabrian Sea (NE Atlantic). Regional Studies in Marine Science, 23, 60-72. doi: 10.1016/j.rsma.2017.10.015 The researchers analyzed the data collection of yearly oceanographic trawl surveys, commercial fishing boat records, and a pop-up satellite archival tag from the Galicia and Cantabrian Seas in order to study the behavior and occurrence of sixgill sharks. Of the sixgill sharks studied, most were juvenile specimens. Most catches occurred in the autumn and winter, with none recorded in the summer. This pattern matches other studies but it is still premature to make definitive conclusions about the seasonality of catches. The study did not find cyclic diel vertical migration patterns which doesn't align with other studies. They attributed this to potential ability differences between the juvenile and adult sharks to swim up and down the water column. Their results also showed that H. griseus prefer temperatures between 8 and 10 degrees.

Griffing, D., Larson, S., Lowry, Dayv., & McNeil, B. (2016). Feeding Behavior of Subadult Sixgill Sharks (Hexanchus griseus) at a Bait Station. PLoS ONE, 11(5). https://doi.org/10.1371/journal.pone.0156730 The study was conducted beneath the Seattle Aquarium pier which is located in Elliot Bay, Puget Sound, Washington at 20 meters of water depth. They used cameras and lights around bait boxes in order to record observations about the feeding behaviors of H. griseus. The factors they considered in determining feeding behavior are the food capture methods used, number of bites per strike, total time of strike in seconds, manipulation techniques utilized, and total time of bait manipulation in seconds. The researchers analyzed 60 strikes and found that sixgill sharks can protrude their upper jaws and vary their methods of feeding depending on the situation. The sharks demonstrated sawing and lateral tearing techniques to manipulate food. Researchers found that the sixgill sharks lower their pectoral fins right before they strike in order to stop forward progressions, making it easier for them to forage. The sharks also showed slow, moderate cranial and mandible activity before they took their first bite. Differences were also seen at different levels. For example, mid-water bait strikes were seen twice as much as benthic water bait strikes. The variability that sixgill sharks possess in their feeding mechanisms could have contributed to their evolutionary success and global distribution.

Meyer, C.G., Nakamura, I., & Sato, K. (2015). Unexpected Positive Buoyancy in Deep Sea Sharks, Hexanchus griseus, and a Echinorhinus cookei. PLoS ONE, 10(6). doi: 10.1371/journal.pone.0127667 The researchers studied the swimming performances of H. griseus and E. cookei using accelerometer-magnetometer data loggers to measure swimming speed, depth, temperature, tri-axial magnetism, and tri-axial acceleration. They recorded data for 36 days of five sixgill sharks and one prickly shark. The data showed that both species swam at depths of 200-300 meters at night and more than 500 meters during the day time. The researchers noticed that during the vertical movements, the deep-sea sharks demonstrated more swimming efforts for the descent than the ascent, as indicated by the greater number of tail beats and their ability to glide upwards for several minutes. This behavior indicates that the sharks are positively buoyant. Positive buoyancy could help the sharks to hunt stealthy by approaching prey from below undetected since their upward gliding permits minimal movement. Another potential benefit has to do with the diel vertical migration. Since the sharks spend their days in colder water, their metabolic rates decline. Positive buoyancy would help them to glide upwards with minimal swimming involved during their evening migrations.

Vella, A., Vella, N. (2017). Population genetics of the deep-sea bluntnose sixgill shark, Hexanchus griseus, revealing spatial genetic heterogeneity. Marine Genomics, 36(SI), 25-32. doi:10.1016/j.margen.2017.05.012 The research focuses on 146 sixgill sharks from around and outside the Mediterranean area and studies the species’ genetic variation, specifically the mitochondrial DNA. The results show that the different populations have various maternal lineages, suggesting that there is genetic heterogeneity in the Mediterranean region. When comparing the mtDNA sequences of H. griseus populations from the Pacific Ocean and those from the Atlantic Ocean, the researchers found that they’re different in the number of repeats within the VNTR region, and they possess unique haplotypes. These genetic differences indicate that different management strategies are needed for the conservation of H. griseus. The researchers turned to historic barriers and female philopatric behaviors to explain these findings. Ice ages drastically changed the sea levels, impacting the ecosystems as a whole. New breeding grounds were also created through historical population expansion during the interglacial period.Jennpark (talk) 23:38, 11 October 2020 (UTC)